If not vacuum processing such as sputtering but a printing process can be used in a process of forming a film such as an insulator film or a conductor film, not only improvement in productivity but also cost reduction due to unnecessity of an expensive film forming apparatus will be expected.
Japanese Patent Application Laid Open No. 2001-51259 (hereinafter referred to as “Patent Literature 1”) discloses that, in a substrate used for a liquid crystal device, a surface protection film which is an insulator film covering an electrode pattern formed as a conductor film on the substrate is formed by flexographic printing. FIGS. 1A, 1B, 2A, and 2B illustrate an insulator film formed by flexographic printing as disclosed in Patent Literature 1. In FIGS. 1A, 1B, 2A, and 2B, reference numeral 11 represents the substrate, reference numeral 12 represents the electrode pattern (conductor film), and reference numerals 13, 13a, and 13b represent a coating film, a lower coating film, and an upper coating film, respectively, each of which is formed with a liquid precursor for forming an insulator film transcribed and applied on the electrode pattern 12.
Patent Literature 1 describes the following technical matters with reference to FIGS. 1A, 1B, 2A, and 2B.
(1) When a liquid precursor is applied by flexographic printing, as illustrated in FIG. 1A, a part in the vicinity of an edge 14 of the coating film 13 is protruded such that the film thickness thereof is approximately twice the film thickness of the inner region of the film, and when the thickness of this protrusion 15 approaches around 1500 Å, cracking occurs on the occasion of cleaning and rubbing treatment. Such cracking causes the coating film 13 to be peeled off. In FIG. 1A, the thickness limit of the surface protection film that can be formed is 750 Å.
(2) As illustrated in FIG. 1B, when a method is employed in which the lower coating film 13a is formed by flexographic printing and then flexographic printing is performed again to form the upper coating film 13b and thereafter the upper coating film 13b and the lower coating film 13a are hardened, cracking occurs on the occasion of cleaning and rubbing treatment afterwards when the thickness of the protrusion 16 in the vicinity of the edge 14 approaches approximately 2000 Å. In FIG. 1B, the thickness limit of the surface protection film that can be formed is 1000 Å.
(3) As illustrated in FIG. 2A, the lower coating film 13a the film thickness of which is about 650 Å is formed, and then, as illustrated in FIG. 2B, the upper coating film 13b the film thickness of which is about 650 Å is formed. At this time, the upper coating film 13b is formed such that an edge 18 of the upper coating film 13b is positioned approximately 200 μm inside from the edge 14 of the lower coating film 13a. A protrusion 17 of the lower coating film 13a does not overlap with a protrusion 19 of the upper coating film 13b. Even at the part at which the sum of the film thickness of the lower coating film 13a and that of the upper coating film 13b is the maximum (namely, where the protrusion 19 is generated), the film thickness is approximately 1950 Å, which is lower than 2000 Å. Accordingly, in FIGS. 2A and 2B, a surface protection film the film thickness of which is 1300 Å can be formed and the film thickness of the part where the protrusion 19 is generated is only approximately 1950 Å. With this, no cracking occurs.
As described above, Patent Literature 1 discloses that, in forming an insulator film by flexographic printing, cracking occurs when a protrusion generated on an edge of the insulator film is thick, and that the insulator film is formed by double coating in which the edges are shifted so that a thick insulator film can be formed and yet occurrence of cracking can be avoided.
Such a protrusion generated when an insulator film is formed by flexographic printing is generated not only on the outer periphery of a printing pattern but also inside the printing pattern. For example, when there is a hole that is a part not printed inside the printing pattern (a blank space in which no ink is transcribed), a protrusion is generated around the hole.
On the other hand, with respect to the insulator film, in addition to the one used as a surface protection film as disclosed in Patent Literature 1, there is one that is formed between two conductor films, for example. When this insulator film formed between two conductor films includes a through hole for connecting the two conductor films and conducting the connected films, the printing pattern is to have a hole corresponding to the through hole. With this, a protrusion is generated around the through hole in the insulator film.
When in the insulator film there is a protrusion around the through hole that is used for connecting the two conductor films, in other words, used for conductor joining and thus the film thickness of the insulator film is large thereat, a conductor joining failure is caused. This will be explained below with reference to the drawings.
FIG. 3A illustrates a schematic structure for the explanation. In this structure, a first conductor film 22, an insulator film 23 and a second conductor film 24 are sequentially layered in order on a substrate 21. In FIG. 3A, reference numeral 25 represents a through hole provided on the insulator film 23 to connect the second conductor film 24 to the first conductor film 22.
FIG. 3B illustrates a cross section of the part of the through hole 25. With a protrusion 23a of the insulator film 23, the film thickness of the insulator film 23 around the through hole 25 is large. With this, the second conductor film 24 is to be formed on a part having a large level difference. For this reason, on the parts surrounded by broken lines in FIG. 3B, defects of the second conductor film 24 which raise problems of electrical conduction continuity are generated, that is, poor electrical connection between the two conductor films due to breaks is generated.
FIG. 3C illustrates a cross section of the part of an outer periphery edge of the insulator film 23 formed on the first conductor film 22. A protrusion 23b of the insulator film 23 causes bleeding of the insulator film 23, and thus causes displacement of the insulator film 23 from the position on which the insulator film 23 is to be formed and impairs the edge linearity of the insulator film 23.